The present invention relates to an alluvial filter candle apparatus and a method of cleaning the same.
Filter candle apparatuses are known in the art, such as described, for example, in the German Design Pat. No. 6,610,766. They serve for filtering of liquids which contain solid matter, or so called muds, whereas filter residues which form a filter cake are withdrawn in the driest possible condition through a discharge outlet in a bottom of the apparatus. In order to clean the filtering apparatus, an inlet of mud or filtrant is throttled down and simultaneously a pressure gas is injected into a filtrant chamber, so that the main part of the residual filtrant is driven out through candle-like filtering elements. The backflow of a filtrate remaining in risers in the interior of the candle-like filtering elements, through the filter cake and thereby repeated moistening of the latter is prevented by a return valve arranged at the lower end of each riser. Separation of the filter cake is performed by pulsating pressure air which is supplied into the interior of the candle-like filtering elements. The above-described filtering apparatus has several disadvantages. The residual filtrant can be driven by the pressure gas only to the level of the lower edges of the permeable means of the candle-like filtering elements. The remaining considerable residual matter runs out when the discharge opening in the bottom of the filter housing is open. The hindrance of the backflow out of the risers is not reliable, inasmuch as solid particles which remain in the filtrate can deposit between the ball and the ball seat of the return valve so that the latter is no longer tight. During filtering of highly viscous liquids, the return valve can be stuck as a result of cooling of the filter cake in condition of the open discharge outlet. Release or separation of the filter cake from the suspended candle-like filtering elements with the aid of the pressure air medium is possible only for very loose filter cake residues. Sticky filter cake residues formed as a circumferentially closed fixed pipes surrounding the candle-like filtering elements cannot be separated from the latter in the above-disclosed manner.